The invention relates to a method for introducing air into the cylinders of an internal combustion (IC) engine, and particularly to charging the cylinder using a displacement supercharger until the desired filling pressure has been reached, and to an engine adapted to use in the method.
Conventional superchargers have been either of the positive displacement or the non-positive displacement type. In the case of a positive displacement supercharger, the operating rate of pumping is a product of the speed of the engine and the displaced volume of the supercharger pumping element. A small displacement of the supercharger may be compensated for by operation at a high speed. Much the same applies for non-positive displacement superchargers, the speed of rotation of an exhaust gas driven turbo-charger being for example about 250,000 rpm, while the engine speed is only 4,000 rpm.
In so-called supercharging a supply of compressed air is produced by a compressor and stored in a storage means. Air flows into the engine cylinder from the storage means every time the cylinder inlet valve is opened. Such a method of supercharging has a relatively high energy requirement, because the energy needed for expulsion of the compressed air into the storage means is many times greater than the energy needed for the compression itself.
For this reason the theory of so-called delayed supercharging has been elaborated, in which a part of the air is drawn in by the piston in the cylinder and another part of the air is compressed by a compressor and expelled into a storage means so that at the right point in time towards the end of the suction stroke of the engine cylinder in question compressed air is transferred through a separate air duct into the cylinder when a pulse generating valve is opened, such air then compressing the air already in the engine cylinder to the required degree. For this to be possible, it is necessary for the additional air to be compressed in relation to the desired filling pressure in the cylinder and furthermore work is preformed in expelling the air into the storage means, although such energy requirement represents an improvement over the so-called supercharging. A further shortcoming is the complex structure in the form of the additional air duct and the means for timing the valve. In addition, the action of expelling the air involves losses, that on the one hand give rise to a still further increase in the energy requirement and on the other hand make their contribution to further heating of the combustion air. More specially in this case of four stroke gasoline engines this makes it necessary means for cooling the combustion air and high drive powers for the supercharging devices that are usually mechanically driven. For this reason delayed supercharging has not come to be accepted in the art.
The object of the invention is to reduce the driving power of the supercharger and limit the increase in temperature during compression to the theoretical minimum. In other words the work needed for expulsion is to be no longer necessary or is to be reduced as far as possible and the costs of producing the system are to be kept low.
In the invention this object is effected by synchronizing the expelling motion of the piston or pistons of the positive displacement supercharger with the motion of the pistons of the engine cylinders to be filled such that the air displaced from the supercharger directly transfers into the engine cylinders in question.
By the method in accordance with this invention, it is no longer necessary for work to be performed for expulsion of the air into the intermediate storage means and it is no longer necessary for there to be compression to a level materially above the pressure in the engine cylinder. There is furthermore no need for the second air duct. The system adopted for causing synchronization between the piston motion of the supercharger and the motion of the piston of the engine is simple.
In keeping with a useful form of the invention, at the beginning of inlet into the engine cylinder, the combustion air flows into the cylinder under atmospheric pressure from the supercharger into the said cylinder and has its pressure gradually increased to the desired filling pressure.
The work performed for filling the cylinder may be still further cut down if, in keeping with a further useful form of the invention, a part of the air to be supplied to the cylinder is drawn in by the piston of the engine and another part thereof is supplied into the cylinder during motion of the piston near bdc (bottom dead center) by the supercharger. In this respect the inlet may be shut if desired for the combustion air after the piston has gone past tdc (top dead center).
In order to perform the method the invention comprises an IC engine, that has at least one piston, moving in a cylinder having an air inlet, and a positive displacement supercharger having an output port thereof joined with the air inlet of the engine, said supercharger having at least one supercharging chamber. In keeping with a first possible form of the invention, the air pumping volume of the supercharger chamber or of the supercharger chambers, is equal to the maximum amount of air needed in the engine cylinder to be charged, and in that there is such a synchronization between the positive displacement supercharger and the motion of the engine piston, that the supercharger expels and compresses the air towards the air inlet when the engine piston is performing the suction stroke.
In a further possible for of the invention the air pumping volume of the supercharger chamber or of the supercharger chambers is equal to the maximum amount of air needed in the engine cylinder to be charged, in addition to an amount of air drawn in by the engine piston for compression to the charging pressure, and in that a synchronization between the positive displacement supercharger and the motion of the engine piston may be so adjusted that the positive displacement supercharger introduces the maximum desired additional amount of air into the engine cylinder while the piston is moving near bdc.
In keeping with a useful form of the invention, the positive displacement supercharger is arranged to be driven by the exhaust gas from the engine; in this respect a further useful development of the invention is possible if the exhaust gas inlet of the positive displacement supercharger is directly connected with the outlet valve of the engine cylinder supplying the exhaust gas. However it also possible for an exhaust gas collector to be placed on the upstream side of the exhaust gas inlet of the positive displacement supercharger and for the exhaust gas side of the supercharging chamber or chambers to be furnished with a pulse controller or generator.
As part of a further useful development of the invention, the positive displacement supercharger is drivingly connected with the crankshaft of the engine and as a further highly useful form of this arrangement there is a belt drive between the crankshaft of the engine and the displacement supercharger such that the ratio between the driving and slack sides of the belt may be varied.
Further useful developments will be seen from the dependent claims in conjunction with the specification. A detailed account of the invention will now follow based on the working examples of the invention to be seen in the figures.